netdev - Re: [PATCH net] netfilter: nfnetlink_queue: acquire rcu_read_lock() in instance_destroy

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Message-ID: <20240515141023.GE13678@breakpoint.cc>
Date: Wed, 15 May 2024 16:10:23 +0200
From: Florian Westphal <fw@...len.de>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Florian Westphal <fw@...len.de>,
	"David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Pablo Neira Ayuso <pablo@...filter.org>,
	Jozsef Kadlecsik <kadlec@...filter.org>, netdev@...r.kernel.org,
	netfilter-devel@...r.kernel.org, coreteam@...filter.org,
	eric.dumazet@...il.com, syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH net] netfilter: nfnetlink_queue: acquire rcu_read_lock()
 in instance_destroy_rcu()

Eric Dumazet <edumazet@...gle.com> wrote:
> > If you prefer Erics patch thats absolutely fine with me, I'll rebase in
> > that case to keep the selftest around.
> 
> I missed your patch, otherwise I would have done nothing ;)
> 
> I saw the recent changes about nf_reinject() and tried to have a patch
> that would be easily backported without conflicts.

Right, makes sense from that pov.
I think its fine to apply the patch in this case, I'll followup later.

Thus:
Acked-by: Florian Westphal <fw@...len.de>

> Do you think the splat is caused by recent changes, or is it simply
> syzbot getting smarter ?

Its old bug, AFAICS your Fixes tag is correct.

1. Userspace prog needs to subscribe to queue x
2. iptables/nftables rule needs to send packets to queue x
3. actual packets that match that have to be sent
4. Userspace program needs to exit while at least one packet
   is queued

Amazing that syzbot managed to hit all 4 checkboxes :)